Theoretically NDEF record payloads are limited in size to 232–1 bytes (the payload length field of the header is four bytes) - of course your Arduino will not support a 4 gigs record, but you should be fine with 4736 bytes.
look at the API for NdefRecord
the type could be TNF_UNKNOWN, which indicates the payload type is unknown but the NFC Forum explains this should be treated similarly to the "application/octet-stream" MIME type.